Apparatus for controlling sheet thickness in continuous strip mills



Jan. I8, 1944. A. sHAYNE ETAL 2,339,359

APPARATUS FOR CONTROLLING SHEET THICKNESS IN CONTINUOUS STRIP MILLS Filed March 20. 1941 Patented Jan. 18, 1944 APPARATUS FOR CONTROLLING SHEET THICKNESS IN CONTINUOUS STRIP MILLS Alexander Shayne and Alexander Zeitlin, New York, N. Y., assignors, by mesne assignments, to Sperry Products, Inc., a corporation of New York Application March 20, 1941, Serial No. 384,268 'z claims. (c1. :3o-35i This invention relates to the continuous rolling of hot strips in a continuous rolling mill. In these mills a short thick slab of metal which is discharged from the furnace at high temperature is passed successively through a series of rolling mill stands, usually l in number, each of which applies pressure to cause repeated thinning out of the material until finally it issues from the No. mill stand as a thin sheet of material several hundred feet in length. It will readily be understood that one of the major objectives in this method of production of sheet material is to obtain as nearly uniform a product, so far as dimensions and crystalline structure are concerned, as possible. Thus it is extremely desirable to obtain a sheet of uniform thickness from one end to the other. This, however, has been found to be extremely difficult. There are various reasons why the thickness of a sheet varies, but chief among these is the taper which results from the fact that the forward end of the strip enters each will stand sooner than the rear end and therefore the forward end is of a higher temperature. Since the amount of deformation is directly proportional to the temperature, it follows that with given pressure exerted between the rolls of any given mill stand, the forward end will be thinned out to a greater degree than the rear end which is cooler. Thus a taper results which in long strips may amount to as much as .020 inch.

It is therefore a principal object of this invention to provide a method and means whereby the thickness of the sheet passing through a continuous rolling mill may be maintained substantially constant from one end thereof to the other. This means will compensate not only for the tendency to taper but will compensate for other causes which may result in non-uniform thickness such as, for example, differences in chemical and crystalline structure in various portions of the sheet.

Further objects and advantages of this invention will become apparent in the following detailed description thereof.

The accompanying drawing is an assembly view, largely diagrammatic, disclosing one form of the invention.

Referring to the drawing, there are shown di'agramrnatically two mill stands which may be numbers 9 and I0 of a continuous rolling mill Awhich would normally comprise ten such stands.

Each stand includes side frame members II and a central cutout portion I2 in which are slidably mounted bearing blocks I3 and I4 which form the Ibearing members for large back-up rollers Il and Il perform the roughing operation of bringing down the thickness of the slab into the form of a sheet. The mill stands 5-I0 inclusive arethe finishing stands which further reduce the sheet to a relatively thin, smooth strip. The slab of metal comes out of the furnace at high temperature and is slid on to conveyor rollers 3| l which are motor driven, and these feed the slab into the mill stands. As the material passes through the pressure rollers it thins out and since it is constrained against any substantial increase in width the thinning causes a very substantial increase in length. The net result of this operation is that the forward end of the strip movesqmuch more rapidly than the rear end, and progressively from the forward end to the rear end the material has increasing time within which toradiate heat and become cooler. As explained in the introduction, this means that with any given pressure between the pressure rollers of the mill stand,

4the forward portion of the strip will tend to be A solution for the problem t'hus presented is to utilize the pressure gauge which measures the pressure existing between the work rolls I9 and 20 of the mill stand as a means for setting into operation means for automatically regulating the pressure to increase or decrease the same as the case may be so as to maintain constant the thickness of the strip. 'Such a pressure gauge is disclosed,`for example, in our copending application, Serial No. 384,212, for Strain gauge for rolling mills and the like, filed March 19, 1941. In said strain gauge a sensitive element 40, `in the form of a wire fixed at one end to the upright frame portion I I andmovable at its other end, is caused to operate an indicator 4I in response to stretching of the frame due to 'pressure between the rolls. Since the pressure between the rolls is a function of the thickness of the strip passing therethrough, it will be understood that as the colder, less deformable portion of the strip passes further apart and hence a greater pressure will be indicated by the indicator. This increase in pressure, over and above what the pressure should be for the required thickness, is caused to operate mechanism which will thin out the strip. If in.- creased pressure were applied to the same mill stand which is indicating the thickness of the strip, it would only result in increased pressure indication in the indicator 4| which would mean that the strip passing therethrough is still thicker than it was before, where actually it is thinner. Therefore, if the sheet is to be thinned out, additional pressure must be applied in one of the preceding mill stands so that the sheet will come to mill stand i8 thinner and will therefore give an indication of lessened pressure, which is the operation desired. Thus, for example, the pressure indicator 4i is on No. I0 mill stand, and the desired pressure is set for a given thickness. Any increase in said pressure means that the strip passing through the work rolls is too thick. It, now, increased pressure is applied Vto the strip on one of the preceding mill stands such as No. 8 mill stand, then the sheet will be thinned out before entering No. I mill stand and the pressure indicator 4| will indicate lessened pressure. The pressure in No. 8 mill stand is increased until the pressure indicator at No. I8 mill stand is the desired pressure and therefore the desired thickness of material. However, the pressure may be increased on No. Ill stand if it is borne in mind that the excess over the desired pressure must be increased in order to thin out the material to the requisite degree.

In order to accomplish the above result, there is actuated from the pressure indicator 4| v a potentiometer contact 50 operating over a resistance 5| so that, asv the index 42 of the pressure indicator rises or falls, the pointer 50 will be rotated around its pivot 52 in one direction or the other. The potentiometer is arranged in parallel across the D. C. supply. A similar potentiometer is arranged in parallel across the same supply and includes a pointer 50 operating over a resistance 5I' similar to resistance 5|-, the said pointer 50 being pivoted at 52' and settable by hand, as for instance by means of knob 53. In the well known manner, when the two potentiometers tap equal portions of the supply, the pointers 50, 50' do not tap an E. M. F.; but when pointer 50 moves above or below the point of equilibrium, due to the fact that the pressure between the work rolls I8 and 20 in mill stand I8 is increasing or decreasing due to thickness of the strip being greater or less than the thickness as determined by the setting of pointer 50', then an E. M. F. is tapped by pointers 50, 50' in one direction or the other, land said E. M. F. after being emplified by amplier A may be caused to operate the screw-downmotor M of mill stand 9 in such di-4 rection as to increase or decrease the pressure between the work rolls I9 and 20. This will thin out or thicken the material passing therethrough and thus will correct the pressure in pressure gauge 4I to a point where pointers 50 and 50' are again in equilibrium. For this purpose the output of amplifier A is cause l to actuate a relay PR which may be of the polarized type, there being a polarizing coil 68 which normally holds an armature 8l in neutral position out of contact with contact 62 or v63 against the action of a spring 64. The output Vfrom ampliiler A acts upon the coil 18 and, depending uponl the direction of the signal, will cause armature 6I to engage contact 62 or contact 83 to close one or the other of two circuits to motor M. One circult lies through central contact 1l and a contact 12, while the other circuit lies through central contact 1| and a contact 13.- Closing the circuit through contact 1I and 12 energizes motor M in a direction to raise the screw 22 and thus relieve the pressure between the work rolls I9 and 20 of the mill stand 8. Closing of the circuit through contacts 1i and 13 energizes the reverse winding of the motor M to operate screw 22 downwardly to increase the pressure between the work rolls and thus thin out the sheet. It will be understood that increase of pressure between the work rolls of mill stand I8 indicating excess thickness oi material will operate pointer 58 in such direction as to close the circuit between contacts 1| and 13 to lower vscrew 22 and increase the pressure to thin out the material. The thinning out will continue until the pressure between the work rolls of millV stand I0 is suillciently reduced to return arm 50 to balanced position where no E. M. F. is developed. Similarly, if the pressure between the work rolls of mill stand l0 decreases, it means the sheet is too thin and contact arm 50 will move in such direction as to close the circuit through contacts 1| and 12 to raise the screw 22 and thus allow thicker strips to pass out of mill stand 8 and into mill stand I0 to increase the pressure between the work rolls of mill stand i0 until such point is reached where arm 50 returns to balanced position.

If no material is passing through the mill stand, then there is a minimum of pressure between the` work rolls of mill stand ID and hence normally the circuit between contacts 1| and 12 would be closed to cause the motor M to'operate screw 22 upwardly. This is undesirable because no material is passing through the mill stands and the thickness control mechanism should not work at this time. In order that the thickness control mechanism shall bel rendered eiective onlywhen material. is passing through the mill stands, there is provided a pivoted lever 88 which normally rests upon the conveyor rolls 3| and is held in contact therewith by spring 8|. 'I'he other end of the lever 88 carries a contact 82 which when nomaterial is passing through the mill stand I8 is out of contact with the cooperating contact member 83. 'I'he said contacts 82 and 83 are in the circuit of the coil 10, and therefore A as long as no material is passing through the mill stands the control device is ineffective and the armature 8| is out of contact with contact 62 or 83. When material passes through the mill stand I Il, it will lift the lower end of lever to cause contacts 82 and 83 to while the device isy described as an automatic l device for controlling thickness, there may be occasions when hand control will be desirable, and therefore there is provided means for quicklytransferring control from the automatic thickness controlling device described above to hand control. For this purpose the contact 1| which is part of the two circuits through the motor M, one circuit including contacts 1I and 12 and the other circuit including the contacts 1| and 13, is itself in contact with thecontact 85 at the lower end of a master control lever 86 pivoted at 81. Aslong as the control lever is in neutral position with contact 85 in engagement with conv tact 1|, the automatic thickness control can operate through circuits lying through 1|, 12 and 1i, 13. However, whenever no control is desired the lever 86 is moved out of the central position so that contact 85 can engage contact 12 or contact 13. Such movement short-circuits the control relay and makes it possible for the motor M to be controlled directly from the master control handle 86.

While the pressure indicator has been described as located on mill stand No. I and controlling the thickness of the sheet by operating the screw-down motor on mill stand No. 9, it will be understood that the pressure indicator on any of the other mill stands may be utilized as the base, provided the screw-down motor on any of the preceding mill stands is controlledthereby.

In accordance with the provisions of the patent statutes, we have herein described the principle and operation of our invention, together with the apparatus which is now considered to represent the best embodiment thereof, but wev desire to have it understood that the apparatus vshown is only illustrative and that the inven-4 tion can be carried out by other equivalent -i said stands which consists in measuring and in V dicating the pressure which exists between the rolls of the respective stands and causing variations from a predetermined indicated pressure in a selected stand to vary the pressure applied to the rolls of a preceding stand in such direction and to such degree that the indicated' pressure in the rst stand'will return to the predeterminedpressure. f

2. In a, continuous rolling mill comprising a plurality of rolling mill stands, each stand comprising a plurality of rolls, means for applying pressure to said rolls and means for indicating the pressure which exists between the rolls,

means for controlling the thickness of material passing between said rolls, said last named f means comprising means whereby variations of said pressure indicating means on a selected stand from a'predetermined indication controls the pressure-applying means of a preceding standv in such direction and to such degree that the indicating means on the selected stand is returned to the predetermined indication.

3. In a continuous rolling mill comprising a plurality of rolling mill stands, each stand comprising a plurality of rolls, means for applying pressure to said rolls and. means for indicating the pressure which exists between said rolls. means for controlling the thickness of material passing between said rolls, said last named means comprising means whereby Variations of said pressure indicating means on a selected stand from a. predetermined indication controls the pressure-applying means of a preceding stand in such direction and to such degree that the indicating means on the selected stand is returned to the predetermined indication, and means whereby said control means is rendered etlective by the passage of material through the rolls of said selected stand. A

4. In a. continuous rolling mill comprising a.

plurality of rolling mill stands, each stand comprising. a plurality of rolls. a reversible screwdown motor for applying pressure to said rolls and means for indicating pressure which exists between the rolls, means for controlling the thickness of material passing between said rolls, said last named means comprising means whereby said indicator causes an electric current to iiow in response to variations from a predetermined indicated pressure in a selected stand, and means whereby said current actuates the screw.- down motor of a preceding stand in such direction and to such degree as to return the indicator of the selected stand to the predetermined indication.

5. In a continuous rolling mill comprising a plurality of rolling mill stands, each stand comprising a plurality of rolls, a reversible screwdown motor for applying pressure to said rolls and means for indicating pressure which exists between the rolls, means for controlling the thickness of material passing between said rolls, said last named means comprising a source of power, a pair of potentiometers arranged in parallel across said source, one of said potentiometers being settable by hand and the other of said potentiometers being operated from an indicator of a selected stand whereby an electric current will be caused to flow when said indicator indicates variations from a predetermined pressure as determined by the setting of said hand-set potentiometer, and means whereby said current actuates the screw-down motor of' a. preceding stand. l

6. In a continuous rolling mill comprising a plurality of rolling mill stands, each stand comprising a plurality of rolls, a reversible screwdown motor for applying pressure to saidrolls and means for indicating pressure which exists between the rolls, means for controlling the thickness of material passing between said rolls, said last named means comprising means whereby said indicator causes an electric current to flow in response to variations from a predeterof a. preceding stand in such direction and to such degree as to return the indicator of the selected stand to the predetermined indication, and

means whereby the circuit traversed by said current is controlled by the passage of material through said selected stand.

7. In a continuous rolling mill comprising a plurality of rolling mill stands, each stand comprising a plurality of rolls, .a reversible screwdown motor for applying pressure to said rolls and means for indicating pressure which exists between the rolls, means for controlling the thickness of material passing between said rolls, said last named means comprising a source of power, apair of potentiometers arranged in parallel across said source, one of said potentiometers being settable by hand and the other of said potentiometers being operated from'an indicator of a selected'stand whereby an electric current will be caused to flow when said indicator indicates variations from the predetermined pressu're, as determined by the setting of said hand-set potentiometer; means whereby said current actuates the screw-down motor of a preceding stand, and'means whereby the circuit traversed by said current is controlled by the passage of material through said selected stand.

ALEXANDER SHAYNE. .lLEXANDER ZEITEN. 

